Industrial technologies used for oxygen or oxygen-rich gas production are based on oxygen separation from air (78 volume percent (vol. %) nitrogen, 21 vol. % oxygen), and include distillation (cryogenic), adsorption and membrane approaches. The cryogenic method for oxygen separation is the most commonly used air separation technology. In this method, air is filtered, compressed, and chilled to the ultra-low (cryogenic) temperature of about −185° C. The cryogenic method reliably produces large quantities of oxygen needed by industry; however, it is complex, expensive and, energy intensive. Other air separation methods used by industry involve nitrogen adsorption on materials such as by zeolites via pressure swing adsorption (PSA), or polymeric/ceramic membranes.
Research to develop/improve oxygen separation targets large-scale (>100 t/day) use by industry. Polymeric membranes are currently limited to the production of oxygen enriched air, with an oxygen concentration of no more than 40 vol. %. The use of high temperature (up to 900° C.) ceramic-based membranes results in increased oxygen purity, but may have technical issues that include significant energy penalty associated with large volume gas heating. The need for new methodology for oxygen production exists which is economical, environmentally friendly, and applicable to large-scale production.
It would be advantageous to provide an alternate method of air separation, for example through repeated aeration and deaeration cycles of water.
Aeration is well known and normally among the first treatment steps employed during the production of drinking water or the treatment of waste waters. Aeration artificially induces gas transfer for the addition of oxygen in order to affect removal of various volatile compounds. Generally in these processes, air bubbles are generated by various processes in liquid-gas mixing vessels, and a swarm of air bubbles provides a large air-to-liquid interface area for separation of soluble surface active substances. In other applications, the swarm of air bubbles functions primarily as a means to increase dissolved oxygen contents in a volume of water, in order to support bacteria or other microorganisms for digestion of biodegradable compounds. These processes are well known, however the gaseous dissolution of oxygen and nitrogen which these processes inherently invoke is not intended to provide an air separation, and the oxygenated waters are typically released to holding vessels where any excess gases release to the atmosphere. Deaeration of water is additionally well known and practiced in applications where dissolved oxygen levels in water are intentionally minimized, such as beverage production and boiler water treatments, however in these deaeration operations, the oxygen removed typically originates as an incidentally introduced constituent, and the gases which evolve during deaeration are generally discarded. Additionally, the deaeration operations typically also utilize a stripping gas such as steam or nitrogen, diluting the concentration of any oxygen which might result. These aeration and deaeration processes have not been integrated in a system whereby an aeration operation followed by a deaeration operation is utilized for the purpose of generating an outlet gas stream having an increased O2 level and decreased N2 level, as is the goal in air separation processes generally.
Provided here is a method for enriching an inlet air stream comprising O2 and N2 by repeated dissolution and subsequent escape of oxygen and nitrogen in water through the use of an enrichment sub-unit conducting sequential aeration and deaeration operations. Within the method, the relationship between the respective Henry's coefficients of the oxygen and nitrogen in water are exploited in order to progressively increase the O2 vol. % in a gas stream to a target O2 vol. %. The method takes advantage of the fact that water has a stronger chemical affinity for O2 than for N2, and generates enriched outlet gas streams by a subsequent degasification of O2 and N2 from aerated water. The method may be conducted generally at room temperature, and allows enrichment of an air stream to a final gas stream comprising over 90 vol. % O2.
These and other objects, aspects, and advantages of the present disclosure will become better understood with reference to the accompanying description and claims.